WO2020121398A1

WO2020121398A1 - Display device and method for manufacturing same

Info

Publication number: WO2020121398A1
Application number: PCT/JP2018/045427
Authority: WO
Inventors: 久幸内海; 仲西　洋平; 昌行兼弘; 翔太岡本; 弘毅今林
Original assignee: シャープ株式会社
Priority date: 2018-12-11
Filing date: 2018-12-11
Publication date: 2020-06-18
Also published as: US12022673B2; CN113243054A; US20220037609A1; CN113243054B

Abstract

A display device (1) includes a positive electrode (22), a negative electrode (25), a QD light emitting layer (24b) that is provided between the positive electrode and the negative electrode, and an ETL (24c) that is provided between the negative electrode and the QD light emitting layer, wherein the ETL comprises metal oxide nanoparticles (NP) and an organic modifier (OM) that covers the surfaces of the nanoparticles and has electron donating characteristics.

Description

Display device and manufacturing method thereof

The present invention relates to a display device provided with an electron transport layer containing metal oxide nanoparticles between a cathode and a light emitting layer, and a manufacturing method thereof.

3A is a diagram showing a laminated structure of a main part of a light emitting element of a conventional display device, and FIG. 3B is a diagram showing a light emitting layer on a light emitting layer of the display device shown in FIG. It is a figure which shows the structure of an electron carrying layer typically. As shown in FIG. 3A, the display device including the quantum dot light emitting diode includes an electron transport layer (hereinafter, referred to as “ETL”) 124c between the quantum dot light emitting layer 124b and the cathode 125. ing. As shown in FIG. 3B, the ETL 124c is formed by spin coating (spinner coating) a dispersion liquid in which nanoparticles NP of metal oxide (generally zinc oxide) are dispersed in a solvent.

Japanese Patent Laid-Open Publication "JP-A-2015-099804"

However, since the nanoparticles NP have small particles, they easily aggregate and have low dispersibility. Therefore, if the ETL124c is formed by applying the above-mentioned dispersion liquid by a spinner, stable film formation cannot be performed, and as shown in FIG. 3B, the formed ETL124c has a non-uniform and flat surface. Will be bad. As a result, the electron transfer of the ETL 124c is biased, and it is highly possible that the ETL 124c does not emit light uniformly.

In addition, for example, in Patent Document 1, in order to improve film adhesion between a transparent resin substrate in an organic electroluminescence element and an inorganic functional layer such as an electrode layer, a barrier layer, and a charge injection/transport layer, the above transparent resin substrate is used. Between the above-mentioned inorganic functional layer and the above-mentioned inorganic functional layer, forming a metal oxide nanoparticle-containing layer in which nanoparticles of a metal oxide surface-treated with a coupling agent such as a silane coupling agent are dispersed in an actinic ray curable resin. Is disclosed.

According to Patent Document 1, by surface-treating the metal oxide nanoparticles with a coupling agent such as a silane coupling agent, the affinity between the metal oxide nanoparticles and the actinic radiation curable resin is increased. Thus, the metal oxide nanoparticles can be uniformly dispersed in the actinic radiation curable resin.

However, the metal oxide nanoparticle-containing layer described in Patent Document 1 is not the electron transport layer itself. Further, the silane coupling agent is not a dopant and cannot transfer electrons. That is, the silane coupling agent does not have a function of receiving an electron and giving it to the metal oxide nanoparticles. Therefore, the metal oxide nanoparticle-containing layer described in Patent Document 1 cannot be used as an electron transport layer.

One embodiment of the present invention has been made in view of the above problems, and an object thereof is that the dispersibility of an electron transporting layer containing nanoparticles of a metal oxide is higher than that of a conventional one, and that the luminous efficiency is superior to that of the conventional one. An object of the present invention is to provide a display device and a manufacturing method thereof.

In order to solve the above problems, the display device according to one embodiment of the present invention includes an anode, a cathode, a light emitting layer provided between the anode and the cathode, and a cathode and the light emitting layer. And an electron transporting layer provided between the nanoparticles, the electron transporting layer including nanoparticles of a metal oxide and an organic modifying agent having an electron donating property and covering the surface of the nanoparticles.

In order to solve the above problems, a method for manufacturing a display device according to one embodiment of the present invention includes an anode, a cathode, a light emitting layer provided between the anode and the cathode, the cathode, and the light emission. An electron-transporting layer provided between the layer and the layer, the electron-transporting layer including nanoparticles of a metal oxide and an organic modifier having an electron-donating property, which covers the surface of the nanoparticles. A method of manufacturing a display device, which comprises: laminating the electron transport layer on the light emitting layer after the light emitting layer is cured.

According to one embodiment of the present invention, it is possible to provide a display device in which the dispersibility of an electron transport layer containing nanoparticles of a metal oxide is higher than before, and which is more excellent in light emission efficiency than before, and a manufacturing method thereof.

(A) is a figure which shows typically an example of the laminated structure of the light emitting element of the display apparatus which concerns on embodiment of this invention, (b) is electron transport on the light emitting layer of the display apparatus shown in (a). It is a figure which shows the structure of a layer typically. It is sectional drawing which shows an example of schematic structure of the display apparatus which concerns on embodiment of this invention. (A) is a figure which shows the laminated structure of the principal part of the light emitting element of the conventional display apparatus, (b) is a structure of the electron carrying layer on the light emitting layer of the display apparatus shown to (a) typically. FIG.

An embodiment of the present invention will be described below with reference to FIGS. 1A and 1B and FIG. 2.

<Display device>
Hereinafter, a case where the display device according to the present embodiment is a QLED display including a quantum dot light emitting diode (hereinafter, referred to as “QLED”) as a light emitting element will be described as an example.

FIG. 1A is a diagram schematically showing an example of a laminated structure of QLEDs in the display device 1 according to the present embodiment. 1B is an electron transport layer (hereinafter, referred to as “ETL”) on the quantum dot light emitting layer (hereinafter, referred to as “QD light emitting layer”) 24b of the display device 1 illustrated in FIG. 1A. It is a figure which shows the structure of 24c typically. FIG. 2 is a cross-sectional view showing an example of a schematic configuration of the display device 1 according to the present embodiment, which includes

QLEDs

5R, 5G, and 5B as light emitting elements.

As shown in FIG. 2, the display device 1 according to the present embodiment has a configuration in which a QLED layer 5 is provided as a light emitting element layer on the array substrate 2. The QLED layer 5 is covered with a sealing layer 6.

The array substrate 2 includes, for example, a lower surface film 10, a resin layer 12, a barrier layer 3, and a TFT layer 4 as a drive element layer.

The lower surface film 10 is, for example, a PET (polyethylene terephthalate) film for realizing a display device having excellent flexibility by sticking the supporting substrate (for example, mother glass) on the lower surface of the resin layer 12 after peeling the supporting substrate. Instead of the lower surface film 10 and the resin layer 12, a solid substrate such as a glass substrate may be used. The resin layer 12 may be made of polyimide, for example. The resin layer 12 may be replaced with a two-layer resin film (for example, a polyimide film) and an inorganic insulating film sandwiched therebetween.

The barrier layer 3 is a layer that prevents foreign matter such as water and oxygen from entering the TFT layer 4 and the QLED layer 5.

A sub-pixel circuit that controls the light emitting element is formed on the TFT layer 4. The TFT layer 4 includes a semiconductor film 15, an inorganic insulating film 16 (gate insulating film) above the semiconductor film 15, a gate electrode GE and a gate wiring above the inorganic insulating film 16, a gate electrode GE and a gate. The inorganic insulating film 18 above the wiring GH, the capacitive electrode CE above the inorganic insulating film 18, the inorganic insulating film 20 above the capacitive electrode CE, and the source wiring SH above the inorganic insulating film 20. The TFT as a drive element is configured to include the semiconductor film 15 and the gate electrode GE, including the wiring including the wiring and the planarization film 21 (interlayer insulating film) above the source wiring SH.

The semiconductor film 15 is made of, for example, LTPS (low temperature polysilicon) or an oxide semiconductor. Although the TFT having the semiconductor film 15 as a channel is shown as a top gate structure in FIG. 2, it may be a bottom gate structure.

The barrier layer 3 and the inorganic

insulating films

16, 18, and 20 are, for example, a silicon oxide (SiOx) film, a silicon nitride (SiNx) film, a silicon oxynitride film (SiNO), which are formed by a CVD (Chemical Vapor Deposition) method. Alternatively, a laminated film of these can be used.

The wirings such as the gate electrode GE, the capacitance electrode CE, and the source wiring SH are, for example, Al (aluminum), W (tungsten), Mo (molybdenum), Ta (tantalum), Cr (chromium), Ti (titanium), Cu( It is composed of a metal single layer film or a laminated film containing at least one of copper).

The flattening film 21 can be made of a coatable photosensitive organic material such as a polyimide resin or an acrylic resin.

The QLED layer 5 is provided with a plurality of QLEDs as light emitting elements. The QLED is formed for each sub pixel corresponding to the sub pixel.

The display device 1 has, for example, a sub-pixel RSP (red sub-pixel) that emits red light, a sub-pixel GSP (green sub-pixel) that emits green light, and a sub-pixel BSP (that emits blue light) as sub-pixels. Blue sub-pixels).

The sub-pixel RSP is provided with a QLED 5R that emits red light as a QLED. The sub-pixel GSP is provided with a QLED 5G that emits green light as a QLED. The sub-pixel BSP is provided with a QLED 5B that emits blue light as a QLED.

Here, red light refers to light having an emission center wavelength in the wavelength band of 600 nm or more and 780 nm or less. Green light refers to light having an emission center wavelength in a wavelength band of more than 500 nm and 600 nm or less. Blue light refers to light having an emission center wavelength in a wavelength band of 400 nm or more and 500 nm or less.

As shown in (a) and FIG. 2 of FIG. 1, each of the QLEDs (

QLEDs

5R, 5G, 5B) has an anode 22 and a hole transport layer (hereinafter referred to as “HTL”) 24a (HTL24aR, HTL24aG, HTL24aB). ), as a light emitting layer, each QD light emitting layer 24b (any one of QD light emitting layer 24bR, QD light emitting layer 24bG, and QD light emitting layer 24bB) having a different wavelength region, and ETL24c (ETL24cR, ETL24cG, ETL24cB), The cathode 25 is laminated in this order from the array substrate 2 side. The anode 22 is electrically connected to each TFT of the array substrate 2.

The QLED 5R includes the HTL 24aR as the HTL 24a, the QD light emitting layer 24bR as the QD light emitting layer 24b, and the ETL24cR (first electron transport layer) as the ETL 24c. The QLED 5G includes the HTL 24aG as the HTL 24a, the QD light emitting layer 24bG as the QD light emitting layer 24b, and the ETL 24cG (second electron transport layer) as the ETL 24c. The QLED 5B includes the HTL 24aB as the HTL 24a, the QD light emitting layer 24bB as the QD light emitting layer 24b, and the ETL 24cB (third electron transport layer) as the ETL 24c.

As shown in FIG. 2, the anode 22, the HTL 24a, the QD light emitting layer 24b, and the ETL 24c in each subpixel are separated into islands for each subpixel by an edge cover 23 that covers the edge of the anode 22. The cathode 25 is not separated by the edge cover 23 and is formed as a common layer common to each sub-pixel.

The anode 22 and the cathode 25 include a conductive material and are electrically connected to the HTL 24a and the ETL 24c, respectively. One of the anode 22 and the cathode 25 is a transparent electrode having a light-transmitting property, and the other is a reflective electrode having a light-reflecting property. When the display device 1 is a top emission type display device that extracts light from the cathode 25 side, the cathode 25 is a transparent electrode, and is, for example, ITO (indium tin oxide), IZO (indium zinc oxide), or AZO. (Aluminum zinc oxide) or GZO (gallium zinc oxide) or the like, and is formed of a light-transmitting conductive material. On the other hand, the anode 22 has, for example, a layer made of such a translucent conductive material and a high visible light reflectance such as Al (aluminum), Cu (copper), Au (gold), or Ag (silver). A laminate of a layer made of a metal or an alloy thereof is used. The display device 1 may be a bottom emission type display device that extracts light from the anode 22 side. In this case, a transparent electrode is used for the anode 22 and a reflective electrode is used for the cathode 25.

In the display device 1, holes and electrons are recombined in the QD light emitting layer 24b by a driving current between the anode 22 and the cathode 25, and excitons generated by the recombination generate quantum dots (semiconductor nanoparticles: hereinafter, " The light is emitted in the process of transition from the conduction band level of QD”) to the valence band level.

The HTL 24a transports holes from the anode 22 to the QD light emitting layer 24b. The HTL 24a may include an inorganic material such as nickel oxide (NiO) or molybdenum oxide (MoO ₃ ), and may be PEDOT (polyethylenedioxythiophene), PEDOT-PSS (poly(3,4-ethylenedioxythiophene). )-Poly(styrene sulfonic acid)), TPD (4,4′-bis[N-phenyl-N-(3″-methylphenyl)amino]biphenyl), PVK (poly(N-vinylcarbazole)), TFB (Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine)]), CBP(4,4 '-Bis(9-carbazoyl)-biphenyl), NPD(N,N'-di-[(1-naphthyl)-N,N'-diphenyl]-(1,1'-biphenyl)-4,4'- An organic material such as a diamine) may be contained. The HTL24aR, HTL24aG, and HTL24aB may be formed of the same material or may be formed of materials having different hole mobilities.

The ETL 24c transports electrons from the cathode 25 to the QD light emitting layer 24b. The ETL 24c will be described in detail later.

The QD light emitting layer 24b emits light by recombination of holes transported from the anode 22 and electrons transported from the cathode 25. In this embodiment, each sub-pixel is provided with a QD of each color as a light emitting material. Specifically, the QD light emitting layer 24bR in the sub pixel RSP has a red QD, the QD light emitting layer 24bG in the sub pixel GSP has a green QD, and the QD light emitting layer 24bB in the sub pixel BSP has a blue QD. In this way, the QD light emitting layer 24b includes a plurality of types of QDs, and the same sub-pixel includes the same type of QDs.

Red QD, green QD, and blue QD are, for example, Cd (cadmium), S (sulfur), Te (tellurium), Se (selenium), Zn (zinc), In (indium), N (nitrogen), P (phosphorus). ), As (arsenic), Sb (antimony), Al (aluminum), Ga (gallium), Pb (lead), Si (silicon), Ge (germanium), and Mg (magnesium). You may include the semiconductor material comprised by the element of.

For the QD light emitting layer 24b, for example, a dispersion liquid in which QD is dispersed in a solvent such as hexane, toluene, octadecane, cyclododecene, or phenylcyclohexane is applied by sub-pixels by a spin coating method, an inkjet method, or the like. As a result, a film can be formed. The dispersion liquid may be mixed with a dispersion material such as thiol and amine.

The sealing layer 6 prevents foreign matter such as water and oxygen from penetrating into the QLED layer 5. The sealing layer 6 includes, for example, an inorganic sealing film 26 that covers the cathode 25, an organic buffer film 27 that is an upper layer than the inorganic sealing film 26, and an inorganic sealing film 28 that is an upper layer than the organic buffer film 27. .. The inorganic sealing film 26 and the inorganic sealing film 28 are each an inorganic insulating film, and are, for example, a silicon oxide (SiOx) film, a silicon nitride (SiNx) film, a silicon oxynitride film (SiNO), which are formed by a CVD method. Alternatively, a laminated film of these can be used. The organic buffer film 27 is a translucent organic film having a flattening effect, and can be made of a coatable organic material such as acrylic. The organic buffer film 27 can be formed by, for example, inkjet coating, but a bank for stopping the droplet may be provided in the non-display area.

<ETL24c>
As shown in (b) of FIG. 1, ETL24c is an organic modified metal oxide in which the surface of metal oxide nanoparticles NP is covered by surface modification with an organic modifying agent OM having an electron donating property. Contains nanoparticles. Therefore, the ETL 24c contains the metal oxide nanoparticles NP and the organic modifier OM having an electron donating property and covering the surface of the nanoparticles NP.

In the present embodiment, “nanoparticles” mean particles having a weight average particle diameter of nanometer size (that is, less than 1 μm). The weight average particle diameter of the nanoparticles NP is preferably in the range of 1 nm to 20 nm because the emission characteristics can be improved, and in the range of 2.5 nm to 12 nm, the electron transfer of ETL24c. It is more preferable because the degree can be improved.

Examples of the metal oxide are selected from the group consisting of ZnO (zinc oxide), TiO ₂ (titanium oxide), MgZnO (magnesium zinc oxide), Ta ₂ O ₃ (tantalum oxide), and SrTiO ₃ (strontium titanium oxide). At least one kind of metal oxide is used. The ETL 24c may include the same kind of metal oxide nanoparticles NP in the sub-pixel RSP, the sub-pixel GSP, and the sub-pixel BSP, and the sub-pixel RSP, the sub-pixel GSP, and the sub-pixel BSP have different types. The metal oxide nanoparticles NP may be included. In other words, the ETL24cR, ETL24cG, and ETL24cB may include nanoparticles NP of the same type of metal oxide, or may include nanoparticles NP of different types of metal oxides. As the metal oxide nanoparticles used for ETL, zinc oxide nanoparticles (hereinafter, referred to as “ZnO—NP”) are common, and they are inexpensive and easily available. Therefore, ZnO-NP is suitable as the nanoparticles NP.

The organic modifier OM is an organic dopant compound capable of donating and accepting electrons and donating electrons to the nanoparticles NP. The nanoparticles NP receive electrons from the cathode 25 via the organic modifier OM and release (transport) the received electrons to the QD light emitting layer 24b. The organic modifier OM is not particularly limited as long as it is a dopant (donor) having an electron donating property. The dopant is used to adjust the concentration of carriers (electrons, holes) and variously control the band structure such as forbidden band width and physical properties by changing the physical properties of the semiconductor crystal. A dopant that is an impurity added to a semiconductor and that supplies electrons to the semiconductor as carriers is called a donor.

Examples of the organic modifier OM include 1,3-bis(carbazol-9-yl)benzene, 4,4′,4″-tri(carbazol-9-yl)triphenylamine, 4,4′- Examples thereof include at least one compound selected from the group consisting of bis(carbazol-9-yl)biphenyl. The ETL24cR, ETL24cG, and ETL24cB may include the same type of organic modifier OM or may include different types of organic modifier OM.

These organic modifiers OM have, for example, a structure having a plurality of benzene rings, and a nitrogen atom bonded to the benzene rings, and by the electron-donating action of the unpaired electrons of nitrogen, the electrons are applied to the nanoparticles NP. To donate.

The above-mentioned organically modified metal oxide nanoparticles can be manufactured by applying various known methods known as surface modification methods for inorganic particles, and the manufacturing method is not particularly limited.

When the metal oxide nanoparticles NP are ZnO—NP, for example, ZnO—NP is recovered by precipitating ZnO—NP by adding hexane to ZnO—NP dispersed in ethanol. A solvent in which the organic modifier OM is dissolved is added to NP, and the mixture is agitated to allow ZnO-NP and the organic modifier OM to coexist, whereby the ZnO-NP is surface-coated with the organic modifier OM. It can be modified. The surface modification in this case is, for example, a chemical bond by a coordinate bond (coordinative bond between the donor and the ZnO—NP by the organic modifier OM), and is carried out at normal temperature under atmospheric pressure. However, the surface modification may be reactive modification, and the temperature, pressure, stirring time, type of stirring device, etc. are not particularly limited.

The ETL24c is a spin coating method (spinner coating) of the solvent containing the metal oxide nanoparticles NP and the organic modifier OM (in other words, a dispersion liquid in which the organic modified metal oxide nanoparticles are dispersed in the solvent). ) Or an ink-jet method or the like for application.

Examples of the solvent include toluene, chlorobenzene, o-dichlorobenzene, phenylcyclohexane, 4-isopropylbiphenyl, 1,1-bis(3,4-dimethylphenyl)ethane and the like. The solvent may be used alone or as a mixture of plural kinds. Since these solvents are volatile and volatilize at room temperature or by heating, the solid film of ETL24c can be easily formed.

According to this embodiment, the dispersibility of the nanoparticles NP in the solvent can be improved by covering the surface of the nanoparticles NP with the organic modifier OM. Therefore, the flatness of the ETL 24c is improved by applying the nanoparticles NP covered with the organic modifier OM by, for example, the spin coating method or the inkjet method as described above.

Further, when a donor is used as the organic modifier OM, when the nanoparticles NP are not covered with the organic modifier OM (in other words, the ETL 24c is a metal oxide of the metal oxide nanoparticles NP and the organic modifier OM). It is possible to increase the number of electrons supplied to the QD light emitting layer 24b as compared with the case where only the nanoparticles NP are included).

The reason for this is as follows. When the surface of the nanoparticles NP is covered with the organic modifier OM (donor), electrons are supplied (injected) from the cathode 25 to the nanoparticles NP, and the electrons are emitted from the nanoparticles NP to the QD emission layer 24b. Then, electrons are supplied to the nanoparticles NP from the donor on the surface of the nanoparticles NP. As a result, the electrons deficient in the emission of the nanoparticles NP are always supplemented. Therefore, there is no shortage of electrons in the QLED. The electrons are also supplied from the cathode 25 to the donor. When the electron is supplied from the cathode 25 to the donor, the electron is supplied from the donor to the nanoparticle NP so as to be extruded, and further, the electron is emitted from the nanoparticle NP to be extruded to the QD emission layer 24b. Therefore, the electrons are exchanged via the donor in this way, so that the mobility (movement speed) of the electrons is increased. The higher the moving speed, the more the number (number) of electrons flowing per unit time. Therefore, by covering the nanoparticles NP with the organic modifier OM, the number of electrons supplied to the QD emission layer 24b can be increased. As described above, in the present embodiment, since the nanoparticles NP are covered with the organic modifier OM having an electron donating property, it is possible to increase the number of electrons supplied to the QD light emitting layer 24b. Therefore, the luminous efficiency of the display device 1 can be improved as compared with the conventional case.

Moreover, it is desirable that the number of holes and the number of electrons in the QD light emitting layer 24b are as close to each other as possible. By matching the number of holes and the number of electrons in the QD light emitting layer 24b, the light emission efficiency is improved. In particular, in recent years, a material having a high hole transport efficiency has been developed as an HTL material. According to this embodiment, even if the HTL 24a is made of a material having a high hole transport efficiency, the QLED does not run out of electrons. Therefore, in this embodiment, it is possible to easily improve the luminous efficiency. In addition, by covering the surface of the nanoparticles NP with a donor and supplying electrons from the donor to the nanoparticles NP to adjust the state so that there is no excess or deficiency of electrons, the number of holes and the number of electrons in the QD light-emitting layer 24b are adjusted. It is also possible to make adjustments so that the numbers substantially match. Therefore, in the present embodiment, it is possible to improve the light emission efficiency more easily.

Further, in the conventional light emitting device, the surface of the nanoparticles NP is not covered with the modifying agent (donor), and the surface of the nanoparticles NP is exposed. Therefore, for example, as shown in FIG. When the material to be the upper layer of the ETL124c is applied thereon, the nanoparticles NP themselves are thermally damaged. In addition, since the surface of the nanoparticles NP is exposed, the nanoparticles (NP) are greatly damaged (deteriorated) by the foreign substances under an active atmosphere (that is, an atmosphere in which foreign substances such as oxygen and water are present). The characteristics deteriorate quickly.

However, according to the present embodiment, by covering the surface of the nanoparticles NP with the organic modifier OM as described above, the nanoparticles NP is damaged by the foreign matter such as water and oxygen under the active atmosphere ( Is less susceptible to deterioration. Therefore, according to the present embodiment, it is possible to provide the display device 1 having higher reliability than the conventional one.

Further, in the conventional light emitting element, as described above, since the surface of the nanoparticles NP is not covered with the modifier (donor), the light emitting element easily aggregates and has low dispersibility. Therefore, in the conventional light emitting device, the barrier effect is low because the spacing between the nanoparticles NP expands depending on the coating state of the dispersion liquid. When the ETL 124c is non-uniform as shown in FIG. 3B, when the material to be the upper layer of the ETL 24c is applied onto the ETL 24c (for example, the cathode 125 is laminated by a method such as sputtering or vapor deposition). When doing so, there is a possibility that thermal damage may occur to the lower layer of the ETL 124c such as the quantum dot light emitting layer 124b.

However, according to this embodiment, when the surface of the nanoparticles NP is covered with the organic modifier OM as described above, when the material to be the upper layer of the ETL 24c is applied onto the ETL 24c (for example, the cathode 25 is The organic modifier OM reduces the thermal damage to the nanoparticles NP itself and the thermal damage to the lower layer of the ETL 24c such as the QD light emitting layer 24b due to the heat (when laminated by a method such as sputtering or vapor deposition). can do. In particular, according to this embodiment, as described above, by covering the surface of the nanoparticles NP with the organic modifier OM, the ETL 24c having high flatness can be formed. Therefore, the lower layer of the ETL 24c is not damaged through the portion where the ETL 24c is thinner than the others. Therefore, according to this embodiment, it is possible to prevent damage to the lower layer of the ETL 24c due to the ETL 24c having a non-uniform film thickness.

As described above, according to the present embodiment, it is possible to provide the display device 1 in which the dispersibility of the electron transport layer containing the nanoparticles of the metal oxide is higher than the conventional one and the luminous efficiency is superior to the conventional one. Further, according to the present embodiment, as described above, the flatness of the electron transport layer containing nanoparticles of the metal oxide can be improved as compared with the conventional one, and the nanoparticles are heated, oxygen, or water. It is possible to provide the display device 1 that can be protected from foreign matter such as.

In the present embodiment, the volume ratio (mixing ratio) of the organic modifier OM to the nanoparticles NP in ETL24c represented by the organic modifier OM/metal oxide nanoparticles NP is 1/99 to 30/70. It is preferably within the range, more preferably within the range of 2/98 to 20/80, and particularly preferably within the range of 10/90 to 20/80. The volume ratio can be easily obtained by, for example, obtaining the diameters of the nanoparticles NP and the organic modifier OM with an SEM (scanning electron microscope).

Table 1 shows that ZnO-NP was used as the nanoparticles NP, 1,3-bis(carbazol-9-yl)benzene was used as the organic modifier OM (donor), and toluene was used as the solvent. Under the same conditions except that the volume ratio between the nanoparticles NP and the donor was variously changed, the above-mentioned volume ratio when the display device having the structure shown in FIG. 2 was manufactured, and the ETL film thickness (average film thickness), ETL The relationship between the film thickness controllability, the surface roughness of ETL, and the external quantum efficiency (EQE) of the display device is shown. In Table 1, sample No. Sample No. 1 is a comparative product. 2 to 8 are products of this embodiment.

In Table 1, the film thickness controllability indicates the difference between the actual film thickness of the ETL film measured by a step gauge and the target film thickness (target film thickness: 60 nm). When the difference between the film thickness of the formed ETL and the target film thickness is within a range of ±1.0 nm or less, it is defined as “⊚”, and the above difference exceeds ±1.0 nm and is within ±5.0 nm. When the difference was within the range of ±5.0 nm or more and ±8.0 nm or less, it was marked with “◯”.

Further, in Table 1, the surface roughness (Rms) shows the magnitude of the surface roughness of ETL measured by an atomic force microscope (AFM), and the case where the surface roughness is less than 3.0 nm is “⊚”. "," when the surface roughness is 3.0 nm or more and 3.5 nm or less, and "△" when the surface roughness exceeds 3.5 nm and 4.0 nm or less. did.

As shown in Table 1, unlike the comparative product, the product of the present embodiment includes the nanoparticles NP and the organic modifier OM having an electron donating property. Therefore, the product of the present embodiment exhibits EQE. It was proved that it was improved over the comparative product.

Further, as shown in Table 1, by setting the volume ratio of the donor to the nanoparticles NP in ETL24c to be 1/99 to 30/70, EQE can be improved more than in the past and a good film can be obtained. It was confirmed that the thickness controllability could be obtained. By adjusting the volume ratio within the range of 10/90 to 20/80, the dispersibility of the organically modified metal oxide nanoparticles (that is, the metal oxide nanoparticles NP covered with the donor) can be improved. It is possible to improve the thickness, controllability of the film thickness can be improved, and since the surface roughness is small, it is possible to form the ETL 24c having a film thickness which is not much different from the target film thickness (target film thickness: 60 nm). Was confirmed.

When the donor component for the nanoparticles is increased as in the case where the volume ratio is 40/40 or 50/50, the thickness of ETL24c becomes slightly thicker than the target thickness, and the film thickness controllability is improved. Although it is low, there is a high possibility that the target film thickness will be approximated by adjusting the solution.

That is, in the above measurement, in order to evaluate the volume ratio, the ETL24c was deposited under the same conditions except that the volume ratio of the nanoparticles NP and the donor was variously changed as described above. When the donor component for the nanoparticles is large, the film thickness controllability is low as compared with the case where the donor component amount for the nanoparticles is small, but as described above, even when the donor component amount for the nanoparticles is large. By changing the film forming conditions, it is possible to bring the film thickness of the ETL 24c close to the target film thickness.

Further, as shown in Table 1, according to the present embodiment, in any of the samples of the present embodiment, the sample No. Compared with the comparative product of No. 1, the surface roughness was low and flat ETL was obtained.

In any case, according to the present embodiment, by covering the surface of the nanoparticles NP with the organic modifier OM, as described above, the dispersibility of the nanoparticles NP in the solvent is improved as compared with the conventional case. It is possible to form the ETL 24c which has higher flatness than the conventional one, is capable of uniform light emission, and has high light emission efficiency. In any case, according to the present embodiment, since the nanoparticles NP are covered with the organic modifier OM (donor), as described above, the number of electrons supplied to the QD emission layer 24b can be reduced. It is possible to increase the number of the nanoparticles NP and the damage to the nanoparticles NP due to the foreign matter under the active atmosphere and the damage to the lower layer of the nanoparticles NP and the ETL 24c due to the heat when the cathode 25 is formed.

Further, in the present embodiment, as described above, the ETL 24c is separately formed in an island shape for each sub pixel. From the viewpoint of luminous efficiency, the volume ratio of the organic modifier OM to the nanoparticles NP is larger in the order of ETL24cB (third electron transport layer), ETL24cG (second electron transport layer), ETL24cR (first electron transport layer). Preferably. In this case, the volume ratio of the organic modifier OM to the nanoparticles NP in ETL24cB is preferably in the range of 2/98 to 10/90, and the organic modifier OM to the nanoparticles NP in ETL24cG is preferable. Is preferably in the range of 10/90 to 20/80, and the volume ratio of the organic modifier OM to the nanoparticles NP in ETL24cR is in the range of 20/80 to 30/70. (However, the above volume ratio satisfies the relationship of ETL24cR>ETL24G>ETL24cB). When the above volume ratio satisfies the above relation and is set within the above range, the luminous efficiency can be controlled.

<Method of manufacturing display device 1>
Next, a method for manufacturing the display device 1 will be described. In the following, a case where a flexible display device is manufactured as the display device 1 will be described as an example.

When manufacturing the flexible display device 1, first, the resin layer 12 is formed on a translucent support substrate (for example, mother glass) not shown. Next, as shown in FIG. 2, the barrier layer 3, the TFT layer 4, the QLED layer 5, and the sealing layer 6 are formed in this order on the resin layer 12. Then, a top film is attached on the sealing layer 6. Then, the supporting substrate is peeled off from the resin layer 12 by irradiation with laser light, the lower surface film 10 is attached to the lower surface of the resin layer 12, and then the lower surface film 10, the resin layer 12, the barrier layer 3, the TFT layer 4, The laminated body including the QLED layer 5 and the sealing layer 6 is divided to obtain a plurality of pieces. Then, a functional film (not shown) is attached to the obtained individual pieces. After that, an electronic circuit board (for example, an IC chip and an FPC) is mounted on a part (terminal portion) of the outside (non-display area, frame) of the display area in which the plurality of sub-pixels are formed. Thereby, the display device 1 is manufactured.

In the step of forming the QLED layer 5, for example, the anode 22, the edge cover 23, the HTL 24a, the QD light emitting layer 24b, the ETL 24c, and the cathode 25 are formed in this order on the TFT layer 4.

In the step of forming the ETL 24c, as described above, for example, a solvent in which the organic modifier OM (donor) is dissolved is added to the metal oxide nanoparticles NP to be surface-modified with the organic modifier OM. A dispersion containing the metal oxide nanoparticles NP is prepared, and the dispersion is applied onto the QD emission layer 24b by, for example, a spin coating method or an inkjet method.

At this time, in the present embodiment, after the QD light emitting layer 24b (any one of the QD light emitting layer 24bR, the QD light emitting layer 24bG, and the QD light emitting layer 24bB) in each sub-pixel is cured, the upper surface of each QD light emitting layer 24b is cured. Then, the corresponding ETL24c (ETL24cR, ETL24cG, ETL24cB) is laminated. This prevents the material of the QD light emitting layer 24b and the material of the ETL 24c from being mixed with each other.

By using an inkjet method for coating the above dispersion liquid, it is possible to coat a narrower range with higher accuracy than, for example, the spin coating method. Therefore, it is possible to form the ETL 24c having high quality with respect to the film thickness and the like.

Also, in this embodiment, the ETL 24c is formed at 150° C. or lower. This prevents the material of the QD light emitting layer 24b from being thermally damaged.

<Modification>
In the above-described embodiment, the case where the light emitting element is a QLED has been described as an example, but the present embodiment is not limited to this. The light emitting element may be, for example, an organic light emitting diode (OLED) or an inorganic light emitting diode.

Further, in the present embodiment, the plurality of types of quantum dots are a combination of red QD, green QD, and blue QD, and the display device 1 includes subpixels RSP, subpixels GSP, and subpixels BSP as subpixels. However, the combination is not necessarily required.

In addition, in the present embodiment, the light emitting element includes the HTL 24a, the light emitting layer (for example, the QD light emitting layer 24b), and the ETL 24c as the functional layers, which are laminated in this order from the anode 22 side between the anode 22 and the cathode 25. Although the case has been described as an example, the functional layer is not limited to the above combination as long as the functional layer includes the light emitting layer and the ETL 24c is provided between the cathode 25 and the light emitting layer. For example, a functional layer other than the above, such as an electron injection layer (EIL), may be further provided between the cathode 25 and the ETL 24c.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each of the embodiments.

1 Display Device 22 Anode 24b, 24bR, 24bG, 24bB QD Light Emitting Layer (Light Emitting Layer)
24c, 24cR, 24cG, 24cB ETL
25 cathode RSP red sub-pixel GSP green sub-pixel BSP blue sub-pixel NP nanoparticles (metal oxide nanoparticles)
OM organic modifier

Claims

An anode, a cathode, a light emitting layer provided between the anode and the cathode, and an electron transport layer provided between the cathode and the light emitting layer,
The display device characterized in that the electron transport layer contains nanoparticles of a metal oxide and an organic modifier having an electron donating property and covering the surface of the nanoparticles.
The organic modifier is 1,3-bis(carbazol-9-yl)benzene, 4,4′,4″-tri(carbazol-9-yl)triphenylamine, 4,4′-bis(carbazol- The display device according to claim 1, which is at least one compound selected from the group consisting of 9-yl)biphenyl.
The display device according to claim 1 or 2, wherein the volume ratio of the organic modifier to the nanoparticles is in the range of 1/99 to 30/70.
A red sub-pixel, a green sub-pixel, and a blue sub-pixel,
The electron transport layer includes a first electron transport layer formed in the red subpixel, a second electron transport layer formed in the green subpixel, and a third electron transport layer formed in the blue subpixel. Including,
4. The volume ratio of the organic modifier with respect to the nanoparticles increases in the order of the third electron transport layer, the second electron transport layer, and the first electron transport layer. The display device according to item.
The volume ratio of the organic modifier to the nanoparticles in the first electron transport layer is in the range of 20/80 to 30/70,
The volume ratio of the organic modifier to the nanoparticles in the second electron transport layer is in the range of 10/90 to 20/80,
The display device according to claim 4, wherein a volume ratio of the organic modifier to the nanoparticles in the third electron transport layer is within a range of 2/98 to 10/90.
The display according to any one of claims 1 to 5, wherein the metal oxide is at least one selected from the group consisting of zinc oxide, titanium oxide, magnesium zinc oxide, tantalum oxide, and strontium titanium oxide. apparatus.
An anode, a cathode, a light emitting layer provided between the anode and the cathode, and an electron transport layer provided between the cathode and the light emitting layer, the electron transport layer is a metal What is claimed is: 1. A method for manufacturing a display device, comprising: oxide nanoparticles; and an organic modifier having an electron donating property, which covers the surface of the nanoparticles.
A method for manufacturing a display device, comprising stacking the electron transport layer on the light emitting layer after the light emitting layer is cured.
The method for manufacturing a display device according to claim 7, wherein the light emitting layer is formed at 150° C. or lower.
The method for manufacturing a display device according to claim 7, wherein the electron transport layer is formed by an inkjet method.